This application is based upon and claims the benefit of Japanese Patent Applications No. 10-329668 filed on Nov. 19, 1998, and No. 11-60283 filed on Mar. 8, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a sensor for detecting a quantity of light, which is applied to an automotive air conditioner, particularly to an air conditioning system capable of independently air-conditioning left and right sides of a vehicle.
2. Description of the Related Art
A so-called zone air-conditioning method (left-light side independently air-conditioning method) is a method for controlling an automotive air conditioner using a sensor, which detects a quantity (intensity) and a direction of solar radiation, to independently air-condition left and right sides in a vehicle compartment.
As the sensor capable of detecting the quantity and direction of solar radiation, a 2D (two elements) type sensor has been developed. Referring to FIG. 22, the 2D type sensor has a left side detecting element (photodetector) 51 disposed at a right side of an axis Lcent, which is a reference of 0xc2x0 in aximuth, and a right side detecting element (photodetector) 52 disposed at a left side of the axis Lcent. A shading member 54 having a through hole 53 is disposed above the detecting elements 51, 52. The right side detecting element 51 and the left side detecting element 52 receive light from the right side and the left side of the axis Lcent, respectively, and output signals corresponding to quantities of light. When azimuth Ø is 0xc2x0, 30xc2x0, 60xc2x0, or 90xc2x0 as shown in FIGS. 24A to 24D, output ratios are as shown in FIG. 23. When azimuth Ø is 0xc2x0, right side and left side output ratios CRR, CRL are 0.50, respectively. The left side and right side output ratios CRL, CRR are represented by the following formulas:
CRL=(left side detecting element output currentxc3x97R)/(the sum of left side and right side detecting element output currentsxc3x97R)
CRR=(right side detecting element output currentxc3x97R)/(the sum of left side and right side detecting element output currentsxc3x97R)
In FIG. 23, shift between the shading member and the photodetectors is zero. Here, a relationship in position between the shading member 54 and the photodetectors 51, 52 is important to exhibit desirable characteristics, and is required to have an assembling accuracy of several tens xcexcm. When positional shift of, for example, 0.1 mm occurs among the members, output ratios are as shown in FIG. 25. In this case, light irradiated parts when azimuth Ø is 0xc2x0, 30xc2x0, 60xc2x0 and 90xc2x0 are as shown in FIGS. 26A to 26D. When azimuth Ø is 0xc2x0, right side and left side output ratios CRR, CRL are 0.60, 0.40, respectively. Thus, when the positional shift occurs between the shading member 54, and the photodetectors 51, 52, there arises a large difference between the left side and right side output ratios, thereby causing malfunctions when left side and right sides in the compartment are independently air-conditioned. Further, requiring high accuracy for processing the parts inevitably results in high cost.
JP-A-7-43145 proposes a technique for forming a shading film by printing black epoxy resin on a transparent substrate disposed above a photodetector. A light transmittance hole is formed at the central portion of the shading film. Accordingly, the shading member is positioned with respect to the photodetector with high accuracy. However, this technique requires to visually recognize the photodetector when the resin is printed, resulting in low workability and low processing yield.
The present invention has been made in view of the above problems. An object of the present invention is to lessen an adverse effect caused by a positional shift between a shading member and a photodetector with desirable detection characteristics.
Here, detection characteristics required for a sensor will be explained. Elevation and azimuth are determined as shown in FIG. 27. FIG. 28 specifically indicates a relationship between the azimuth and a quantity of heat received by a vehicle when the sun moves from the front to the right side of the vehicle with the elevation of 40xc2x0. The quantity of heat received by the vehicle becomes the maximum when the azimuth is 60xc2x0, and decreases in the order of 90xc2x0, 30xc2x0, and 0xc2x0 azimuths. When the azimuth is in a range of 0xc2x0 to 30xc2x0, the change in quantity of heat received by the vehicle is small, and sunlight is delivered uniformly to passengers. With this azimuth range, it is assumed that a difference in quantity of solar radiation between the left side and the right side is small. On the other hand, when the azimuth is larger than approximately 30xc2x0, the difference in quantity of solar radiation aimed to the passengers is large.
Accordingly, as shown in FIG. 29, it is desirable for the sensor that sensor outputs from the right and left sides are approximately equal to each other when the azimuth is in a range of 0xc2x0 to 30xc2x0, and abruptly change (increase or decrease) when the azimuth is in a range of 30xc2x0 to 60xc2x0. That is, the difference between the outputs from the right and left sides is not required when light enters from a vehicle front with the azimuth in a range of 0xc2x0 to 30xc2x0. The difference between the outputs from the right and left sides is required to be large when the azimuth is larger than approximately xc2x130xc2x0.
To achieve the above object with the desirable characteristics, according to the present invention, a sensor for detecting a quantity of light has a housing having an axis along a direction in which light enters the sensor when an azimuth is zero. The axis divides a surface of the housing into a first region and a second region. A first photodetector is disposed on the second region of the housing, and a second photodetector is disposed on the first region of the housing. A central photodetector is further disposed on both the first region and the second region across the axis. A sensitivity of the central photodetector is lowered as compared to those of the first and second photodetectors. A first quantity of light entering the sensor from a side of the first region is cooperatively detected by the first photodetector and the central photodetector, and a second quantity of light entering the sensor from a side of the second region is cooperatively detected by the second photodetector and the central photodetector.
Accordingly, when the sensor is mounted on a vehicle to detect quantities of light incident on right and left seats of the vehicle, the right and left seats can be independently air-conditioned based on the quantities of light detected by the sensor. In addition, because the sensitivity in the vicinity of the axis is blunted (lowered) by the central photodetector having a low sensitivity, even if a positional shift occurs between a shading member disposed above the housing and the photodetectors, output signals corresponding to the first and second quantities of light are less susceptible to the positional shift.
In other words, when the azimuth is small, light is incident on the vicinity of the axis. In this case, a difference between the output signals corresponding to the first and second quantities of light is small. When the azimuth increases, the difference between the output signals also increases, thereby approaching ideal detection characteristics.
When the detection of the quantities of light is performed without using the central photodetector, the first photodetector has a plurality of first protrusions protruding from the second region toward the first region across the axis, and the second photodetector has a plurality of second protrusions protruding from the first region toward the second region across the axis. The plurality of first protrusions extend on the first region with a first width from the axis together with the plurality of second protrusions, and the plurality of second protrusions extend on the second region with a second width from the axis together with the plurality of first protrusions. Accordingly, the sensitivity of the vicinity of the axis is blunted, thereby achieving the effects described above.